Process of manufacturing alpha cellulose



Patented Nov. 4, 1930 PATENT OFFICE LAUBI I. L. DURCHMAN, F PETERSB URG, VIRGINIA PROCESS OF MANUFACTURING ALPHA CELLULOSE No Drawing.

My said invention relates to a new and useful method of manufacturing cellulose suitable for making of highgrade alphacellulose using the well known sulphate process with some alterations regarding used chemicals, cooking-time, temperature and pressure. The usual sulphate cooking process is a very drastic one by reason of the short cooking time and strong chemicals used, but for making kraftpulp it is satisfactory and commercial. For making an easy bleaching sulphate pulp with highest possible percentage of alphacellulose the chips, independent ofwhat kind of wood is 'used, have to be digested under certain conditions. of time, temperature and pressure with a composition of white and black liquors. As is well known, in the usual sulphate process the cooking proceeds for about three to three and one-half hours. Accord.-

ing to my process cooking proceeds for from three to six hours. To prevent an oxidation of the fiber a certain amount of sodium sulphite (Na sO between 0.8-1.0% based on added. This amount of Na,S O is necessary if the Na S in the white liquor is lower than -35 gr. per liter. If the digesting operation has been a careful one the percentage of al hafiber may be found between 90-95%.

Ihus obtained easy bleaching sul hate cellulose contains a large amount 0 incrustpounds. I have found that with boiling the.

cellulose in an open tank, or under ressure and using 2-6% of NaOH, or was water with the same amount of NaOH from the strong caustic treatment which will be described later and 26% of common salt (NaGl) base on the dry weight of the cellulose under certain conditions of temperathe air dry weight of the chips has to be Application-filed May 8, 1929. Serial No; 361,546.

ture and time a very easy bleaching cellulose can be obtained. The boiling time in an open tank is between three andsix hours. The alkaline salts react with the incrusting substances partly dissolving and partly decomposing them into watersoluble compounds. After the cellulose has been thoroughly washed and thickened it'is bleached.

The alkaline bleaching solution which contains from to of NaOH based upon the amount of bleaching powder used and which is added to the dry bleaching powder before adding water gives a somewhat slower bleaching but results in a highgrade bleached cellulose. The resence of alkali prevents a too quick bleac ing and dissolves incrusting substances. A multiple stage bleaching operation is preferable because it gives a very satisfactory bleaching result, with a considerably smaller loss in the alphacellulose percentage. The first stage is a chlorination of the incrusting matters and the second stage a dissolving of the incrusting and coloring matters. It is of great advantage to take of the necessary total bleaching solution into the first stage of bleaching. After the chlorine is exhaustedand the cellulose thoroughly washed the second part or the last is added. The temperature can be raised after 2 to 3 hours of bleaching to 40-45 C. After the bleaching is finished the cellulose is thorou hly washed and thickened to highest possi le dryness, and then the strong alkaline treatment with NaOH solution is given for about 5 hours at about room temperature. Bleached cellulose as above mentioned has after the bleaching 8992% of alphacellulose. Depending upon the grade of desired percentage of alphacellulose in the finished pulp, the strength of the NaOH solution is based. Using a solution with 542% of NaOH under certain time, temperature and consistency an alphacellulose as high as 99% can be obtained. To recover the caustic liquor the cellulose has to be centrifuged and the first and second washwater saved for reuse (for the first boiling treatment) or to be taken for recovery with the black liquor.

' dry weight of the cellulose, which precipitates the main compound calcium, into calcium oxalate and dissolves the iron the treatment being continued for 3 to 5 hours at about room temperature. Theoxalic acid can be recovered to about 80-90% if the cellulose is centrifuged. Thus recovered oxalic acid;has to be filtered and strengthened up with fresh oxalic acid and can be reused. A very thorough washing after the oxalic treatment is necessary because the fiber has a great afiinity to absorb alkaline and acid salts and precipitates.

My preferred process may be illustrated in a flow sheet as follows:

Flow sheet I. Digesting the wood chips with white and black liquor and 0.81.0% of Na SO based on airdry weight of the chips for easy bleaching pulp.

Black liquors to recovery. Washing, screening and thickening of easy bleaching pulp. Contains 92-94% alphacellulose.

. Di esting of the-pulp in open tank with 2-6% of. NaOH and 2.-6% of NaCl based on the airdry weight of .the pulp.

Washing and thickening,

III.

Bleaching, washing and centrifuging.

Treatment with 5- 12% NaOH based on the airdry weight of the pulp. Washing and centrifuging.

V. Tre utment with 6-8% oxailc'acid on base of the airdry 1 weight of the pulp. Washing and centrifuging. -Qx'alic acid recovered l for reuse. VI. Drying pt the pulp.

1. First wash water for open tank digesting.

2. Recover strong caustic liquor for reuse.

weight of the wood chips and continuing the cooking for a longer period than is the usual practice in the sulphate process, and boiling the resultant pulp under atmospheric pressure with a solution containing 26% sodium hydroxide and 26% of common salt.

3. A process for producing alphacellulose which consists in cooking wood chips. with black and white sulphate liquor with the addition of sodium sulphite in the proportion of 0.81.0% based on the airdry weight of the wood chips, boiling the resultant pulp under atmospheric pressure with a mixture containing 26% sodium hydroxide and 26% common salt, bleaching, and treating the bleached pulp at room temperature for three to six hours with a 512% solution of sodium hydroxide.

4. A process for producing alphacellulose which consists in cooking wood chips with black and white sulphate liquorwith the addition of sodium sulphite in the pro ortion of 0.8-1.0% based on the airdry weight of the wood chips, boiling the resultant'pulp under atmospheric pressure with a mixture containing sodium hydroxide and common salt, bleaching, treating the bleached pulp at room temperature for three to six hours with a 512% solution of sodium hydroxide, recovering the sodium hydroxide, washing, and treating with oxalic acid to neutralize the residual alkali and to facilitate extraction of other residual and coloring impurities.

In testimony whereof I afiix my signature.

LAURI I. L. DURGHMAN.

Having thus fully described m said ini I vention, what I claim as new an desire to secure by Letters Patent, is:

1. A process for producing easi bleaching cellulose which consists in coo ing Wood chips with black and white sulphate liquor with the addition of sodium sulphite in the proportion of 0.8-1.0% based on the airdry weight of the Wood chips, continuing the cooking for a longer period than is the'usual practice in the sul hate process, thereby increasing the alp acellulose content, and treating the pulp with a solution containing 2-{3t%' sodium hydroxide and 26% common sa 7 2. A process for producing easy bleachin cellulose which consists in cooking woo chips with black and white sulphate liquor with the addition of sodium sulphite in the proportion of 0.8-1.0% based on the airdry 

